PSI - Issue 84

D. Di Fiore et al. / Procedia Structural Integrity 84 (2026) 159–166

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The range between 0 and 20% is considered below the minimum level of service. Using the forecast level of defect, the preliminary risk SGG+SLO assessment is also updated for each year of analysis allowing a detailed inspection schedule (according to Fig. 2) that can be used to evaluate operative costs.

Fig. 2. Inspection frequencies in accordance with the LLGG and function of the SGG+SLO preliminary risk assessment

Each simulation is performed on a user-defined time window, the output is including economics (CapEx, OpEx, TotEx), structural performance in terms of number of sections in a condition equal or below 20% of the theoretical original one both for SGG and SLO mechanism of failure and, finally, carbon footprint and social impact (cost of the wasted time due to traffic). 2.3. Intervention strategies and impact on conditions The following four intervention strategies are usually compared, with the aim of determining which is most effective, but any kind of intervention can be theoretically analysed: • To Do Nothing – no refurbishment work carried out. Tunnel management is limited to maintenance and periodic inspection of the asset in order to ensure the minimum safety levels. • IMS – Extraordinary Maintenance Intervention – interventions aimed at reducing local structural vulnerability and mitigating localised water ingress without a significant impact on the global behaviour of the structure (see section type in Fig. 3). These interventions do not prolong the Useful Life of the tunnel, although, depending on the context, they can guarantee their long-term functionality according to the purposes for which they are designed. • IRS – Structural Reinforcement Intervention –Capable of increasing the strength of the structure to mainly local, but also global, mechanisms of failure (see typical section in Fig. 4); this type of intervention prolongs Useful Life (depending on the type of intervention and the context) for periods ranging between 10 and 50 years. • TRS – Tunnel Renewal Strategy – Regeneration of the tunnel's final linings using innovative techniques and technologies and high-performance materials (see typical section in Fig. 5). These interventions prolong the Useful Life of the tunnel of at least 50 years.